Motile bacteria such as Escherichia coil are attracted by certain chemicals and repelled by others, a process known as chemotaxis. In addition, these bacteria are attracted by certain physical stimuli and repelled by others: for example, 1) light brings about phototaxis; 2) temperature, thermotaxis; and 3) osmolarity, osmotaxis. Work proposed in this application aims to understand how these physical stimuli function to bring about these behavioral responses. In the case of chemicals, the stimuli are sensed by some twenty different chemoreceptors. These send their information to four different transducers called Methyl-accepting Chemotaxis Proteins the MCPs; in some cases the chemoreceptors actually are the MCPs. In a process known as excitation, MCP by way of phosphorylated or dephosphorylated chemotaxis (Che) proteins tells the flagella whether to rotate counterclockwise and thus bring about running in the case of attractants, or whether to rotate clockwise and thus bring about tumbling in the case of repellents. Then excitation is shut off (even though the attractant or repellent is still present) by a process known as adaptation: This consists of a change in the level of methylation of MCP. In the case of physical stimuli, work reported here and experiments proposed here aim to find out if this same mechanism also applies. It appears that in certain cases it might while in other cases this mechanism is bypassed. Physical stimuli have been and will be identified, and how the responses occur have partially been or will be elucidated. The mechanisms discovered here will hopefully have relevance to understanding neurobiology and behavior in higher organisms, including man. Further, diseases of the nervous system can perhaps be understood by results of the kinds found here.